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Re: Why am I getting this error?
*To*: mathgroup at smc.vnet.net
*Subject*: [mg60352] Re: Why am I getting this error?
*From*: Paul Abbott <paul at physics.uwa.edu.au>
*Date*: Wed, 14 Sep 2005 03:27:19 -0400 (EDT)
*Organization*: The University of Western Australia
*References*: <dg69s7$a9j$1@smc.vnet.net>
*Sender*: owner-wri-mathgroup at wolfram.com
In article <dg69s7$a9j$1 at smc.vnet.net>, ksmath <kdsimon at uiuc.edu>
wrote:
> I am attempting to solve a system with 3 pde's and I keep getting this error
> even though I think all of my equations have independent variables:
>
> NDSolve::dvnoarg: The function v appears with no arguments.
>
> If anyone could find the mistake in my code I would really appreciate it.
> C,V, and R are the dependent variables, and t (time) and x(distance-does not
> depend on time) are the independent variables. All other variables are
> constants.
Some comments:
[1] Although your equations are impossible to read due to some
mysterious symbols, the equation involving r appears to be completely
decoupled from the equations involving c and v -- so solve this one
first.
[2] You are using the symbols r and v as subscripts as well as using
them as the names of functions in the pde's. This could cause problems
(unless you "symbolize" such subscripted symbols using the Notation
package).
[3] To use NDSolve, all parameters must resolve to numerical values.
There are a number of parameters in your equations for which no
numerical values are defined or implied.
[4] In the NDSolve command, you are solving for functions q1 and q2 --
these are not defined.
Since you are at UIUC, I suggest that you attend the upcoming Wolfram
Research TechConf <http://www.wolfram.com/news/events/techconf2005/>.
There will be a number of helpful sessions on solving differential
equations using Mathematica. In addition, at the Training tab, you will
see there are several Wolfram Education Group sessions that are likely
to be of interest.
Cheers,
Paul
> Thank you for any assistance you can provide me.
>
> \!\(\(rRHS\ = \ \(d\_r\) D[r[t,
> x], {x, 2}] + Î² \((1 - \((r[t, x] - r\_base)\)/\((k\_r -
> r\_base)\))\) \((r[t, x] - r\_base)\);\)\[IndentingNewLine]
> \(vRHS\ = \ \(d\_v\) D[v[t, x], {x, 2}] - Ï?\ v[t, x]\ -
> Î·\ v[t, x]\ c[t, x]/\((Î³\_1 + v[t, x])\) + If[
> q\_large < q\_min, Î» \((q\_large - q\_min)\), 0];\)\[IndentingNewLine]
> \(\(cRHS\ = \ D[c[t, x]\ v[t, x]\ D[v[t, x], x], x] + If[v[
> t, x] â?¥ v\_g, Ï?\ v[t, x]\ c[t,
> x]\ /\((Î³\_2 +
> v[t, x])\), Ï? \((v[t, x] -
> v\_d)\) c[t, x]];\)\(\[IndentingNewLine]\)
> \)\[IndentingNewLine]
> \(reqn\ = D[r[t, x], t]\ == \ rRHS;\)\[IndentingNewLine]
> \(veqn\ = \ D[v[t, x], t]\ == \ vRHS;\)\[IndentingNewLine]
> \(ceqn\ = \ D[c[t, x], t]\ == \ cRHS;\)\)
>
> BC1 = Derivative[0, 1][r][t, 0] == 0;
> BC2 = Derivative[0, 1][r][t, 1] == 0;
> BC3 = Derivative[0, 1][v][t, 0] == 0;
> BC4 = Derivative[0, 1][v][t, 1] == 0;
> BC5 = c[t, 0] == 1;
> BC6 = c[t, 1] v[t, 1] Derivative[0, 1][v][t, 1] == 0;
>
> \!\(\(c\_init = \(c\_o\) Exp \((\(-150\) x\^2)\) == c[0,
> x];\)\[IndentingNewLine]
> \(r\_init = \((K\_r -
> r\_base)\) Exp \((\(-100\) x\^2)\) + r\_base == r[0, x];\)\
> \[IndentingNewLine]
> \(v\_init = \((v\_g - v\_d)\)/\((2 v\_o)\) == v[0, x];\)\)
>
> \!\(\(solution\ = \ NDSolve[{reqn, \ veqn, \ ceqn, q1\_i,
> q2\_i, \ c\_init, \ v\_init, \
> r\_init, \ BC1, \ BC2, \ BC3, \ BC4, \ BC5, \ BC6}, {r[t, x], v[t,
> x], c[t, x], q1[t, x], q2[t, x]}, {t, 0, 1}, {x, 0, 1}];\)\)
>
> Any help is much appreciated.
>
> Katie
_______________________________________________________________________
Paul Abbott Phone: 61 8 6488 2734
School of Physics, M013 Fax: +61 8 6488 1014
The University of Western Australia (CRICOS Provider No 00126G)
AUSTRALIA http://physics.uwa.edu.au/~paul
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